【跟着于老师学C/C++】5.4 allocate-merrory-c++style

突发奇想，记录下来，一来纪念，纪念这段有目标有方向的路，二来自己复习用。

视频连接点这

C ： malloc free

• 仅仅是申请一段内存，然后将指针返回。
  c++:
• 不仅仅是申请一段内存。

//allocate an int, default initializer(do nothing)
int * p1 = new int;

new是操作符，new int是表达式，结果是内存的地址。

初始化，可以理解为默认的初始化，对于new int的初始化为啥都不干，初始化了个寂寞啊。

//allocate an int, initialized to 0
int * p2 = new int();

初始化0。

//allocate an int, initialized to 5
int * p3 = new int(5);

初始化为5.

更复杂的。（更复杂的功能后面会介绍）

//allocate an int, initialized to 0
int * p4 = new int{};//c++11
//allocate an int, initialized to 5
int * p5 = new int{5};//c++11

看看怎么初始化结构体的。C++中的结构体和类几乎完全等价。

//allocate a Student class, default initializer
Student * ps1 = new Student;
//allocate a Student class, initialize the members
Student * ps2 = new Studeng{"Yu", 2020, 1};//c++11 

? class中的默认初始化是怎么错的。？（后面再来回答）

//allocate 16 int, default initializer(do nothing)
int * pa1 = new int[16];
//allocate 16 int, zero initialized
int * pa2 = new int[16]();
//allocate 16 int, zero initialized
int * pa3 = new int[16]{};//c++11
//allocate 16 int, the first 3 elements are initialized to 1,2,3, the rest 0
int * pa4 = new int[16]{1, 2, 3};

//allocate memory for 16 Student objects, default initializer
Student * psa1 = new Student[16];
//allocate memory for 16 Student objects, the first two elements are initialized
Student * psa2 = new Student[16]{{"Shao",1989,1},{"Nian", 1990,2}};

为类成员数组申请内存，会调用类成员默认的初始化

//deallocate memory
delete p1;
//deallocate memory
delete ps1;

//deallocate the memory of the array
delete pa1;
//deallocate the memory of the array
delete []pa2;

//deallocate the memory of the array， and call the destructor of the first element
delete pa1;
//deallocate the memory of the array, and call the destructors of all the elements
delete []psa2;

[]的区别，

• 如果是int数组，delete 和delete[]是没有区别的，但是对于结构体数组，就有区别了。都会释放掉内存，但是delete只会调用第一个元素的析构函数，delete []会调用所有元素的析构函数。
• **只要是数组，就写成delete [] 最安全 **。

• Operateor new is similar with malloc() but with more features
• …